Methods of manufacturing multi-element thermoelectric alloys

ABSTRACT

Disclosed is a method of forming a multi-element thermoelectric alloy. A plurality of binary alloys and milling balls are put in a milling pot to perform a ball-milling process to obtain a multi-element thermoelectric alloy powders. The milling balls have a diameter of 1 mm to 10 mm. The milling balls and the binary alloys have a weight ratio of 1:1 to 50:1. The rotation rate of the ball-milling process is of 200 rpm to 1000 rpm. The ball-milling process is processed for 4 hours to 12 hours.

CROSS REFERENCE TO RELATED APPLICATIONS

This Application claims priority of Taiwan Patent Application No. 100148813, filed on Dec. 27, 2011, the entirety of which is incorporated by reference herein.

TECHNICAL FIELD

The disclosure relates to thermoelectric materials, and in particular relates to methods for manufacturing the same.

BACKGROUND

A thermoelectric material can be controlled to move the internal carriers thereof, thereby directly transferring heat to electricity (or electricity to heat) without a mechanical moving part. The thermoelectric material is applied to temperature differential power generation, waste heat recovery, electronic component cooling, air condition system, and the likes. The electricity/heat conversion efficiency of the thermoelectric material is usually represented as the thermoelectric figure of merit (ZT value). ZT=S²σT/κ, wherein S is the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature, and κ is thermal conductivity. The ZT value is positively correlated to high electricity/heat conversion efficiency. The ZT value of the thermoelectric material can be increased by increasing the electrical conductivity (σ), increasing the Seebeck coefficient (S), or decreasing the thermal conductivity (κ) of the thermoelectric material.

The multi-element thermoelectric alloy powders can be prepared from an alloy rod or element powders. In a process of manufacturing the alloy rod, the element ratio of alloy rod will not match a predetermined element ratio due to the melting of the raw materials at a high temperature, in which some elements may evaporate. In the thermoelectric alloy researches, the powders from the alloy rods result in the interactions of the defects during ball-milling, such that the thermoelectric property of the product is reduced. For example, a p-type BiSbTe alloy will be milled to produce too much electrons due to the interaction of anti-site defects and vacancies during ball-milling, thereby reducing the thermoelectric property of a product. To avoid the above problems of the alloy rod, the element powders may be directly mechanically ball-milled for a long period to manufacture a multi-element thermoelectric alloy. However, the ball-milling for alloying the element powders takes up much time, e.g. dozens of hours. In addition, it is difficult to get the sufficiently uniform alloy powders by this method, and therefore the application value of the method utilizing the element powders is reduced.

Accordingly, novel methods of manufacturing multi-element thermoelectric alloy powders and thermoelectric materials are called-for.

SUMMARY

One embodiment of the disclosure provides a method of manufacturing a multi-element thermoelectric alloy, comprising: providing a plurality of binary alloys and milling balls in a milling pot to perform a ball-milling process to obtain the multi-element thermoelectric alloy powders, wherein the milling balls have a diameter of 1 mm to 10 mm, the milling balls and the binary alloys have a weight ratio of 1:1 to 50:1, the ball-milling process has a rotation rate of 200 rpm to 1000 rpm, and the ball-milling process is processed for 4 hours to 12 hours.

A detailed description is given in the following embodiments with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:

FIG. 1 shows X-ray diffraction spectra of multi-element thermoelectric alloy powders in Examples and Comparative Examples of the disclosure;

FIG. 2 shows the ZT value to temperature curves of thermoelectric bulk materials in Examples and Comparative Examples of the disclosure;

FIG. 3A shows X-ray diffraction spectra of a multi-element thermoelectric alloy powder and a thermoelectric bulk material in Comparative Examples of the disclosure;

FIG. 3B shows a partial enlarged diagram of FIG. 3A;

FIG. 4 shows the ZT value to temperature curves of thermoelectric bulk materials in Comparative Examples of the disclosure;

FIG. 5A shows X-ray diffraction spectra of thermoelectric bulk materials in Examples and Comparative Examples of the disclosure; and

FIG. 5B shows a partial enlarged diagram of FIG. 5A.

DETAILED DESCRIPTION

Below, exemplary embodiments will be described in detail with reference to accompanying drawings so as to be easily realized by a person having ordinary knowledge in the art. The inventive concept may be embodied in various forms without being limited to the exemplary embodiments set forth herein. Descriptions of well-known parts are omitted for clarity, and like reference numerals refer to like elements throughout.

In one embodiment, different compound powders such as binary alloys are adopted to prepare multi-element alloys. For example, a combination of binary alloys Bi₂Te₃ and Sb₂Te₃ can be ball-milled with high energy to form a ternary alloy powder, Bi_(x)Sb_(2-x)Te₃, wherein x is a value of 0.1 to 0.8. In one embodiment, x is a value of 0.3 to 0.6. A combination of binary alloys Bi₂Te₃ and Bi₂Se₃ can be ball-milled with high energy to form a ternary alloy powder, Bi₂Se_(y)Te_(3-y), wherein y is a value of 0.1 to 0.8. A combination of binary alloys PbTe and SnTe can be ball-milled with high energy to form a ternary alloy powder, Pb_(z)Sn_(1-z)Te, wherein z is a value of 0.1 to 0.9. In one embodiment, z is a value of 0.6 to 0.9.

In other embodiments, a combination of binary alloys PbTe and AgSb, a combination of binary alloys PbAg and Sb₂Te₃, or a combination of binary alloys PbSb and AgTe can be ball-milled with high energy to form a quaternary alloy powder, Ag_(m)Pb_(n)Te_(p)Sb, wherein m is a value of 0.1 to 1, n is a value of 15 to 25, and p is a value of 15 to 25. Still in this embodiment, other metal compounds such as PbI₂, TeI₄, SbI₂, or AgI can be added a little to modify the Pb, Te, Sb or Ag element ratio of the quaternary alloy Ag_(m)Pb_(n)Te_(p)Sb. A combination of binary alloys PbAg and PbSb and a metal compound TeI₄, a combination of binary alloys PbAg and PbTe and a metal compound SbI₂, a combination of binary alloys PbTe and PbSb and a metal compound AgI, or a combination of binary alloys AgTe and AgSb and a metal compound PbI₂ can be ball-milled with high energy to form a quinary alloy powder, Ag_(m)Pb_(n)Te_(p)SbI_(q), wherein m is a value of 0.1 to 1, n is a value of 15 to 25, p is a value of 15 to 25, and q is a value of 0.1 to 1.

The ball-milling process is a critical point of the disclosure. A suitable ball-milling energy is beneficial for forming a stable and uniform multi-element thermoelectric alloy powder. The ball-milling process can be performed by rotation, stirring, attrition, and/or vibration. In one embodiment, a plurality of binary alloy and milling balls are put into a milling pot, and then ball-milled in argon to obtain a multi-element thermoelectric alloy powder. The milling balls can be stainless, and have a diameter of 1 mm to 10 mm. Overly small milling balls will not provide enough impact energy during the ball-milling process, thereby forming multi-element thermoelectric alloy powder with a poor alloying degree. Overly large milling balls will limit the refinement degree of the ball-milling process. The milling balls and the binary alloys have a weight ratio of 1:1 to 50:1. An overly high weight ratio of the milling balls will cause an overly low milling energy due to an overly short motion path of the milling balls. An overly low weight ratio of the milling balls will also cause an overly low milling energy due to overly few collisions between the milling balls. The ball-milling process has a rotation rate of 200 rpm to 1000 rpm, or of about 300 rpm to 600 rpm. An overly high rotation rate will cause an overly high ball-milling energy, such that the content loss of ball-milled powders increases. An overly low rotation rate will cause the low alloying degree of ball-milled powders. The ball-milling process is processed for 4 hours to 12 hours, or of about 5 hours to 10 hours. The overly short ball-milling period will cause raw binary alloys residue without further alloying due to incomplete alloying. An overly long ball-milling period will produce too much reverse carriers due to the overly long period of the defect interaction.

Subsequently, the mentioned multi-element thermoelectric alloy powders can be sintered by spark plasma sintering (SPS) to form a disorder nano-structure thermoelectric bulk alloy, which would have the internal phonon scattering, low thermal conductivity, and high electrical conductivity. The alloying process may obtain the thermoelectric alloy powders with high alloying degree in a short period. The spark plasma sintering is a fast powder sintering process. Therefore, this manufacturing process of multi-element thermoelectric bulk alloys has the potential to be applied in mass production. Different compound powders can be collocated with the above alloying processes to prepare a multi-element thermoelectric alloy with a high ZT value, flexibility of modifying the content of a product, and alloy content stability.

The spark plasma sintering (SPS) is a critical point of the disclosure. In one embodiment, the multi-element thermoelectric alloy powder formed by the ball-milling is sintered and compressed by the SPS in argon or vacuum to obtain a thermoelectric bulk material. The spark plasma sintering process is performed at a temperature of 300° C. to 600° C. An overly high SPS temperature will cause the powders to be easily melted to result in content loss. An overly low SPS temperature will not sinter the sintered powder densely due to too many void defects existing in the microstructure. The spark plasma sintering process is performed for a period of 3 minutes to 30 minutes. An overly long SPS period will cause the nano grains to disappear due to the increase of the grain size in the sintered bulk material. An overly short SPS period will not completely dense the sintered bulk due to many void defects existing. The SPS has a heating rate of 25° C./minute to 100° C./minute from room temperature to a processing temperature. An overly slow heating rate of the SPS will cause the nano grains to disappear due to the grain growth during sintering. In the SPS process, the multi-element thermoelectric alloy powders are compressed by a pressure of 25 MPa to 100 MPa. An overly low compressing pressure will lower the powder sintering density. An overly high compressing pressure will make the grain structure in the sintered alloy to have the obvious orientations, thereby influencing the alloy properties according to the grain orientations.

After the ball-milling and SPS processes, a thermoelectric bulk material is obtained. The described processes have advantages as below:

(1) High alloying degree and uniformity: binary alloys and other metal compounds (high stability and no defect/void/impurity) can be ball-milled for a period of less than 10 hours to obtain a multi-element thermoelectric alloy powders with high alloying degree and uniformity.

(2) Reducing the interaction of defects: in high energy ball-milling process, it may reduce internal defects, voids, defect interaction, and reverse carriers of the alloy product by milling the binary alloys and other metal compounds. As such, the electrical conductivity of the alloy product will be not reduced by the reverse carriers.

(3) Nano-structure effect: the high energy mechanical ball-milling process not only alloys different compound powders, but also manufactures the alloy powders with nano grains. The powders can be rapidly sintered by an electrical current, in which a pulse current passes through the powder interfaces to form high energy plasma. The rapid sintering may remove oxides on the powder surface to form a complete interface between the grains and keep the nano grain structure. A nano inclusion will be precipitated to grain boundaries and the inside of grains by a sintering current effect. The nano-inclusion can cause the quantum effect and enhance Seebeck coefficient. Simultaneously, the phonons should have the scattering effect due to the nano grains and nano grain boundaries in the microstructure, thereby efficiently reducing the thermal conductivity to enhance thermoelectric conversion efficiency.

(4) Process stability and energy saving: the compound powders serving as starting materials have the excellent chemical stability. It will be difficult to result in content loss during the ball-milling and sintering processes at high temperatures. As such, the content ratio of the product is easily controlled, and the process stability is enhanced. The compound powders adopted to prepare the multi-element thermoelectric alloy powders can be ball-milled for a short period to obtain the powders with high alloying degree. The alloyed powders can be rapidly sintered by the temperature lower than that of a conventional alloy melting and the heat-pressing method. In addition, the alloyed powders can be rapidly sintered for several minutes. Accordingly, the rapid sintering process of the disclosure may largely decrease the process period to save energy.

EXAMPLES Comparative Example 1 Bi_(0.4)Sb_(1.6)Te₃ Alloy Rod

A Bi_(0.4)Sb_(1.6)Te₃ alloy rod prepared by the alloy melting method was crushed and then put into a ball-milling pot to perform a ball-milling process in argon to obtain the multi-element thermoelectric alloy powders. An X-ray diffraction spectrum of the multi-element thermoelectric alloy powders is shown in FIG. 1. The milling balls were stainless balls having a diameter of 3 mm. The milling balls and the Bi_(0.4)Sb_(1.6)Te₃ alloy had a weight ratio of 20:1. The rotation rate of the ball-milling process was 600 rpm. The ball-milling process was performed for 9 hours.

The multi-element thermoelectric alloy powders were put into a sintering mold, and the sintering mold was cold compressed to be molded by a clamping machine.

The molded multi-element thermoelectric alloy powders were then put into a spark plasma sintering equipment (SPS, SYNTEX INC., DR.SINTER Model: SPS-511S) to perform a sintering process in argon at a temperature of 400° C. for 10 minutes to obtain a thermoelectric bulk material, wherein the heating rate from room temperature to the processing temperature was 100° C./minute. During the sintering process, the molded multi-element thermoelectric alloy powders were compressed by a pressure of 100 MPa. The thermoelectric bulk material had the ZT value to temperature curve as shown in FIG. 2.

Example 1

4 molar parts of Sb₂Te₃ (commercially available from Alfa Aesar) and 1 molar part of Bi₂Te₃ (commercially available from Alfa Aesar) were put into a ball-milling pot to perform a ball-milling process in argon to obtain the multi-element thermoelectric alloy powders Bi_(0.4)Sb_(1.6)Te₃. An X-ray diffraction spectrum of the multi-element thermoelectric alloy powders Bi_(0.4)Sb_(1.6)Te₃ is shown in FIG. 1. The milling balls were stainless balls having a diameter of 3 mm. The milling balls and the binary alloys (Sb₂Te₃ and Bi₂Te₃) had a weight ratio of 20:1. The rotation rate of the ball-milling process was 600 rpm. The ball-milling process was performed for 9 hours.

The multi-element thermoelectric alloy powders were put into a sintering mold, and the sintering mold was cold compressed to be molded by a clamping machine.

The molded multi-element thermoelectric alloy powders were then put into a spark plasma sintering equipment (SPS, SYNTEX INC., DR.SINTER Model: SPS-511S) to perform a sintering process in argon at a temperature of 400° C. for 10 minutes to obtain a thermoelectric bulk material, wherein the heating rate from room temperature to the processing temperature was 100° C./minute. During the sintering process, the molded multi-element thermoelectric alloy powders were compressed by a pressure of 100 MPa. The thermoelectric bulk material had the ZT value to temperature curve as shown in FIG. 2.

Example 2

4 molar parts of Sb₂Te₃ (commercially available from Alfa Aesar) and 1 molar part of Bi₂Te₃ (commercially available from Alfa Aesar) were put into a ball-milling pot to perform a ball-milling process in argon to obtain the multi-element thermoelectric alloy powders Bi_(0.4)Sb_(1.6)Te₃. An X-ray diffraction spectrum of the multi-element thermoelectric alloy powders Bi_(0.4)Sb_(1.6)Te₃ is shown in FIG. 1. The milling balls were stainless balls having a diameter of 3 mm. The milling balls and the binary alloys (Sb₂Te₃ and Bi₂Te₃) had a weight ratio of 30:1. The rotation rate of the ball-milling process was 600 rpm. The ball-milling process was performed for 9 hours.

The multi-element thermoelectric alloy powders were put into a sintering mold, and the sintering mold was cold compressed to be molded by a clamping machine.

The molded multi-element thermoelectric alloy powders were then put into a spark plasma sintering equipment (SPS, SYNTEX INC., DR.SINTER Model: SPS-511S) to perform a sintering process in argon at a temperature of 400° C. for 10 minutes to obtain a thermoelectric bulk material, wherein the heating rate from room temperature to the processing temperature was 100° C./minute. During the sintering process, the molded multi-element thermoelectric alloy powders were compressed by a pressure of 100 MPa. The thermoelectric bulk material had the ZT value to temperature curve as shown in FIG. 2.

As shown in FIG. 1, the binary alloys Bi₂Te₃ and Sb₂Te₃ were ball-milled and alloyed to form the multi-element alloy powders having a similar crystallization structure as the Bi_(0.4)Sb_(1.6)Te₃ alloy rod. In addition, the multi-element alloy powders formed by ball-milling had an excellent alloying degree.

Example 3

4 molar parts of Sb₂Te₃ (commercially available from Alfa Aesar) and 1 molar part of Bi₂Te₃ (commercially available from Alfa Aesar) were put into a ball-milling pot to perform a ball-milling process in argon to obtain the multi-element thermoelectric alloy powders Bi_(0.4)Sb_(1.6)Te₃. An X-ray diffraction spectrum of the multi-element thermoelectric alloy powders Bi_(0.4)Sb_(1.6)Te₃ is shown in FIG. 1. The milling balls were stainless balls having a diameter of 3 mm. The milling balls and the binary alloys (Sb₂Te₃ and Bi₂Te₃) had a weight ratio of 30:1. The rotation rate of the ball-milling process was 600 rpm. The ball-milling process was performed for 9 hours.

The multi-element thermoelectric alloy powders were put into a sintering mold, and the sintering mold was cold compressed to be molded by a clamping machine.

The molded multi-element thermoelectric alloy powders were then put into a spark plasma sintering equipment (SPS, SYNTEX INC., DR.SINTER Model: SPS-511S) to perform a sintering process in argon at a temperature of 400° C. for 5 minutes to obtain a thermoelectric bulk material, wherein the heating rate from room temperature to the processing temperature was 100° C./minute. During the sintering process, the molded multi-element thermoelectric alloy powders were compressed by a pressure of 50 MPa. The thermoelectric bulk material had the ZT value to temperature curve as shown in FIG. 2.

As shown in FIG. 2, the thermoelectric bulk material in the Examples had a better ZT value than that of the thermoelectric bulk material in the Comparative Example 1.

Comparative Example 2

3 molar parts of Sb₂Te₃ (commercially available from Alfa Aesar) and 1 molar part of Bi₂Te₃ (commercially available from Alfa Aesar) were put into a ball-milling pot to perform a ball-milling process in argon to obtain the multi-element thermoelectric alloy powders Bi_(0.5)Sb_(1.5)Te₃. An X-ray diffraction spectrum of the multi-element thermoelectric alloy powders Bi_(0.5)Sb_(1.5)Te₃ is shown in FIG. 3A. The milling balls were stainless balls having a diameter of 3 mm. The milling balls and the binary alloys (Sb₂Te₃ and Bi₂Te₃) had a weight ratio of 20:1. The rotation rate of the ball-milling process was 300 rpm. The ball-milling process was performed for 3 hours.

The multi-element thermoelectric alloy powders were put into a sintering mold, and the sintering mold was cold compressed to be molded by a clamping machine.

The molded multi-element thermoelectric alloy powders were then put into a spark plasma sintering equipment (SPS, SYNTEX INC., DR.SINTER Model: SPS-511S) to perform a sintering process in argon at a temperature of 350° C. for 5 minutes to obtain a thermoelectric bulk material, wherein the heating rate from room temperature to the processing temperature was 100° C./minute. During the sintering process, the molded multi-element thermoelectric alloy powders were compressed by a pressure of 100 MPa. The X-ray diffraction spectrum of the thermoelectric bulk material is shown in FIG. 3A, and the ZT value to temperature curve is shown in FIG. 4.

Comparative Example 3

3 molar parts of Sb₂Te₃ (commercially available from Alfa Aesar) and 1 molar part of Bi₂Te₃ (commercially available from Alfa Aesar) were put into a ball-milling pot to perform a ball-milling process in argon to obtain the multi-element thermoelectric alloy powders Bi_(0.5)Sb_(1.5)Te₃. The milling balls were stainless balls having a diameter of 3 mm. The milling balls and the binary alloys (Sb₂Te₃ and Bi₂Te₃) had a weight ratio of 20:1. The rotation rate of the ball-milling process was 300 rpm. The ball-milling process was performed for 3 hours.

The multi-element thermoelectric alloy powders were put into a sintering mold, and the sintering mold was cold compressed to be molded by a clamping machine.

The molded multi-element thermoelectric alloy powders were then put into a spark plasma sintering equipment (SPS, SYNTEX INC., DR.SINTER Model: SPS-511S) to perform a sintering process in argon at a temperature of 400° C. for 5 minutes to obtain a thermoelectric bulk material, wherein the heating rate from room temperature to the processing temperature was 100° C./minute. During the sintering process, the molded multi-element thermoelectric alloy powders were compressed by a pressure of 100 MPa. The X-ray diffraction spectrum of the thermoelectric bulk material is shown in FIG. 3A. As shown in FIG. 3B, an enlarged diagram of a dotted circle 41 in FIG. 3A, two diffraction peaks mean that the sintered thermoelectric bulk material had an insufficient alloying degree due to the low energy ball-milling process.

Comparative Example 4

3 molar parts of Sb₂Te₃ (commercially available from Alfa Aesar) and 1 molar part of Bi₂Te₃ (commercially available from Alfa Aesar) were put into a ball-milling pot to perform a ball-milling process in argon to obtain the multi-element thermoelectric alloy powders Bi_(0.5)Sb_(1.5)Te₃. The milling balls were stainless balls having a diameter of 3 mm. The milling balls and the binary alloys (Sb₂Te₃ and Bi₂Te₃) had a weight ratio of 20:1. The rotation rate of the ball-milling process was 300 rpm. The ball-milling process was performed for 3 hours.

The multi-element thermoelectric alloy powders were put into a sintering mold, and the sintering mold was cold compressed to be molded by a clamping machine.

The molded multi-element thermoelectric alloy powders were then put into a spark plasma sintering equipment (SPS, SYNTEX INC., DR.SINTER Model: SPS-511S) to perform a sintering process in argon at a temperature of 300° C. for 5 minutes to obtain a thermoelectric bulk material, wherein the heating rate from room temperature to the processing temperature was 100° C./minute. During the sintering process, the molded multi-element thermoelectric alloy powders were compressed by a pressure of 100 MPa. The thermoelectric bulk material had the ZT value to temperature curve as shown in FIG. 4. As shown in FIG. 4, the thermoelectric bulk material formed by the low energy ball-milling process and the SPS process had a ZT value of a little higher than 0.4, which was obviously less than the ZT value of the thermoelectric bulk material in the Examples.

Comparative Example 5

3 molar parts of PbTe (commercially available from Aldrich) and 1 molar part of SnTe (commercially available from Alfa Aesar) were put into a ball-milling pot to perform a ball-milling process in argon to obtain the multi-element thermoelectric alloy powders. The milling balls were stainless balls having a diameter of 3 mm. The milling balls and the binary alloys (PbTe and SnTe) had a weight ratio of 20:1. The rotation rate of the ball-milling process was 300 rpm. The ball-milling process was performed for 1 hour.

The multi-element thermoelectric alloy powders were put into a sintering mold, and the sintering mold was cold compressed to be molded by a clamping machine.

The molded multi-element thermoelectric alloy powders were then put into a spark plasma sintering equipment (SPS, SYNTEX INC., DR.SINTER Model: SPS-511S) to perform a sintering process in argon at a temperature of 300° C. for 5 minutes to obtain a thermoelectric bulk material, wherein the heating rate from room temperature to the processing temperature was 100° C./minute. During the sintering process, the molded multi-element thermoelectric alloy powders were compressed by a pressure of 100 MPa. The X-ray diffraction spectrum of the thermoelectric bulk material is shown in FIG. 5A.

Comparative Example 6

3 molar parts of PbTe (commercially available from Aldrich) and 1 molar part of SnTe (commercially available from Alfa Aesar) were put into a ball-milling pot to perform a ball-milling process in argon to obtain the multi-element thermoelectric alloy powders. The milling balls were stainless balls having a diameter of 3 mm. The milling balls and the binary alloys (PbTe and SnTe) had a weight ratio of 20:1. The rotation rate of the ball-milling process was 300 rpm. The ball-milling process was performed for 1 hour.

The multi-element thermoelectric alloy powders were put into a sintering mold, and the sintering mold was cold compressed to be molded by a clamping machine.

The molded multi-element thermoelectric alloy powders were then put into a spark plasma sintering equipment (SPS, SYNTEX INC., DR.SINTER Model: SPS-511S) to perform a sintering process in argon at a temperature of 400° C. for 5 minutes to obtain a thermoelectric bulk material, wherein the heating rate from room temperature to the processing temperature was 100° C./minute. During the sintering process, the molded multi-element thermoelectric alloy powders were compressed by a pressure of 100 MPa. The X-ray diffraction spectrum of the thermoelectric bulk material is shown in FIG. 5A.

Comparative Example 7

3 molar parts of PbTe (commercially available from Aldrich) and 1 molar part of SnTe (commercially available from Alfa Aesar) were put into a ball-milling pot to perform a ball-milling process in argon to obtain the multi-element thermoelectric alloy powders. The milling balls were stainless balls having a diameter of 3 mm. The milling balls and the binary alloys (PbTe and SnTe) had a weight ratio of 20:1. The rotation rate of the ball-milling process was 300 rpm. The ball-milling process was performed for 3 hours.

The multi-element thermoelectric alloy powders were put into a sintering mold, and the sintering mold was cold compressed to be molded by a clamping machine.

The molded multi-element thermoelectric alloy powders were then put into a spark plasma sintering equipment (SPS, SYNTEX INC., DR.SINTER Model: SPS-511S) to perform a sintering process in argon at a temperature of 300° C. for 5 minutes to obtain a thermoelectric bulk material, wherein the heating rate from room temperature to the processing temperature was 100° C./minute. During the sintering process, the molded multi-element thermoelectric alloy powders were compressed by a pressure of 100 MPa. The X-ray diffraction spectrum of the thermoelectric bulk material is shown in FIG. 5A.

Example 4

3 molar parts of PbTe (commercially available from Aldrich) and 1 molar part of SnTe (commercially available from Alfa Aesar) were put into a ball-milling pot to perform a ball-milling process in argon to obtain the multi-element thermoelectric alloy powders. The milling balls were stainless balls having a diameter of 3 mm. The milling balls and the binary alloys (PbTe and SnTe) had a weight ratio of 20:1. The rotation rate of the ball-milling process was 300 rpm. The ball-milling process was performed for 6 hours.

The multi-element thermoelectric alloy powders were put into a sintering mold, and the sintering mold was cold compressed to be molded by a clamping machine.

The molded multi-element thermoelectric alloy powders were then put into a spark plasma sintering equipment (SPS, SYNTEX INC., DR.SINTER Model: SPS-511S) to perform a sintering process in argon at a temperature of 300° C. for 5 minutes to obtain a thermoelectric bulk material, wherein the heating rate from room temperature to the processing temperature was 100° C./minute. During the sintering process, the molded multi-element thermoelectric alloy powders were compressed by a pressure of 100 MPa. The X-ray diffraction spectrum of the thermoelectric bulk material is shown in FIG. 5A. FIG. 5B shows a partial enlarged diagram of FIG. 5A.

Example 5

3 molar parts of PbTe (commercially available from Aldrich) and 1 molar part of SnTe (commercially available from Alfa Aesar) were put into a ball-milling pot to perform a ball-milling process in argon to obtain the multi-element thermoelectric alloy powders. The milling balls were stainless balls having a diameter of 3 mm. The milling balls and the binary alloys (PbTe and SnTe) had a weight ratio of 20:1. The rotation rate of the ball-milling process was 300 rpm. The ball-milling process was performed for 6 hours.

The multi-element thermoelectric alloy powders were put into a sintering mold, and the sintering mold was cold compressed to be molded by a clamping machine.

The molded multi-element thermoelectric alloy powders were then put into a spark plasma sintering equipment (SPS, SYNTEX INC., DR.SINTER Model: SPS-511S) to perform a sintering process in argon at a temperature of 400° C. for 5 minutes to obtain a thermoelectric bulk material, wherein the heating rate from room temperature to the processing temperature was 100° C./minute. During the sintering process, the molded multi-element thermoelectric alloy powders were compressed by a pressure of 100 MPa. The X-ray diffraction spectrum of the thermoelectric bulk material is shown in FIG. 5A. FIG. 5B shows a partial enlarged diagram of FIG. 5A.

Different compound powders (e.g. binary alloys) were directly alloyed to form the multi-element thermoelectric alloy in the Examples. Because the compound powders were more stable than pure element powders, the compound powders were ball-milled with high energy to form the multi-element thermoelectric alloy powders with little content variation. In other words, the ball-milling problem such as content loss or defect interaction can be avoided by utilizing the compound powders. The parameters of the high energy ball-milling process can be controlled to increase the stability and uniformity of the processes for manufacturing the multi-element thermoelectric alloy powders, which is good for controlling of the alloy content, reducing the process period, and increasing the alloying degree of products. The thermoelectric bulk materials of the Examples had several advantages such as a maximum ZT value which was greater than 0.4 and a short ball-milling period. Furthermore, the thermoelectric alloy powders had a high alloying degree.

It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed embodiments. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents. 

What is claimed is:
 1. A method of manufacturing a multi-element thermoelectric alloy, comprising: providing a plurality of binary alloys and milling balls in a milling pot to perform a ball-milling process to obtain a multi-element thermoelectric alloy powder, wherein the milling balls have a diameter of 1 mm to 10 mm, the milling balls and the binary alloys have a weight ratio of 1:1 to 50:1, the ball-milling process has a rotation rate of 200 rpm to 1000 rpm, and the ball-milling process is processed for 4 hours to 12 hours.
 2. The method as claimed in claim 1, wherein the binary alloys comprise a combination of Bi₂Te₃ and Sb₂Te₃, and the multi-element thermoelectric alloy powder is Bi_(x)Sb_(2-x)Te₃, wherein x is a value of 0.1 to 0.8.
 3. The method as claimed in claim 1, wherein the binary alloys comprise a combination of Bi₂Te₃ and Bi₂Se₃, and the multi-element thermoelectric alloy powder is Bi₂Se_(y)Te_(3-y), wherein y is a value of 0.1 to 0.8.
 4. The method as claimed in claim 1, wherein the binary alloys comprise a combination of PbTe and SnTe, and the multi-element thermoelectric alloy powder is Pb_(z)Sn_(1-z)Te, wherein z is a value of 0.1 to 0.9.
 5. The method as claimed in claim 1, wherein the binary alloys comprise a combination of PbTe and AgSb, a combination of PbAg and Sb₂Te₃, or a combination of PbSb and AgTe, and the multi-element thermoelectric alloy powder is Ag_(m)Pb_(n)Te_(p)Sb, wherein m is a value of 0.1 to 1, n is a value of 15 to 25, and p is a value of 15 to
 25. 6. The method as claimed in claim 5, further adding a metal compound into the milling pot, wherein the metal compound comprises PbI₂, TeI₄, SbI₂, or AgI.
 7. The method as claimed in claim 1, further adding a metal compound into the milling pot, wherein the metal compound comprises PbI₂, TeI₄, SbI₂, or AgI.
 8. The method as claimed in claim 7, wherein the binary alloys and the metal compound comprise a combination of PbAg, PbSb, and TeI₄, a combination of PbAg, PbTe, and SbI₂, a combination of PbTe, PbSb, and AgI, or a combination of AgTe, AgSb, and PbI₂, and the multi-element thermoelectric alloy powder is Ag_(m)Pb_(n)Te_(p)SbI_(q), wherein m is a value of 0.1 to 1, n is a value of 15 to 25, p is a value of 15 to 25, and q is a value of 0.1 to
 1. 9. The method as claimed in claim 1, further comprising sintering and compressing the multi-element thermoelectric alloy powder in argon or vacuum by a spark plasma sintering process, thereby forming a multi-element thermoelectric bulk alloy, wherein the spark plasma sintering process is performed at a temperature of 300° C. to 600° C. for a period of 3 minutes to 30 minutes.
 10. The method as claimed in claim 9, wherein the spark plasma sintering process has a heating rate of 25° C./minute to 100° C./minute, and the multi-element thermoelectric alloy powder is compressed by a pressure of 25 MPa to 100 MPa. 